Ceramic matrix composite (CMC) structures are often used in aerospace and other applications due to their ability to withstand relatively high operating temperatures such as, for example exhaust gases, gases encountered upon re-entry into the Earth's atmosphere, etc. Further, various CMC's have been used to fabricate monocoque structures, or sandwich structures that use foam, tile, truss or honeycomb core constructions, for example. While monocoque structures tend to be thin and lightweight, they exhibit low bending stiffness and cannot efficiently react to normal bending loads. Monocoque structures also exhibit poor stability and can buckle under relatively low compressive loads. Sandwich structures can have much higher bending stiffness with a minimal weight impact and are thus desirable for many structural applications. The fabrication of ceramic composite sandwich structures, and the incorporation of thermal insulation within these structures present several challenges and has been a topic of recent research.
Some sandwich structures made of ceramic matrix composites are processed using multiple matrix slurry infiltration and pyrolysis steps. Presently known solutions involve wrapping previously fabricated insulation with ceramic fabric impregnated with ceramic slurry that could wick into underlying insulation during layup or subsequent matrix infiltration cycles. To convert the ceramic prepreg to a rigid matrix composite, the wrapped insulation is typically sintered or heated at temperatures exceeding from about 2000° F. to about 2800° F. This can result in shrinkage and a coefficient of thermal expansion (CTE) mismatch between the CMC outer skin and the insulation, degradation of the insulation leading to cracking and poor insulation performance, loss of insulating and damping benefits, etc. Other sandwich structures have been prepared using high temperature metals such as steels, titaniums, and nickel based alloys, etc. through hot forming and expansion. Previously, because of the nature of the forming process, insulation and bulk absorbers could not be added during fabrication. In these types of structures, insulating blankets have sometimes been bonded or attached to one side, but are not able to be integrated within the sandwich structure.